Thank you very much for your question. It is our pleasure to answer it.

In the name of Allah, We praise Him, seek His help and ask for His forgiveness. Whoever Allah guides none can misguide, and whoever He allows to fall astray, none can guide them aright.

Dear brother, you should know that Duha Prayer is not obligatory rather it is an emphatic sunnah (highly recommended) due to the most reliable view among scholars. 

The time of Duha begins after the sun fully rises and it ends approximately 15 minutes before Dhuhr prayer. The most preferred time for Duha prayer is at the hottest part of the day, when the sun has reached its zenith (its highest point), and this is approximately halfway between sunrise and Dhuhr prayer. The Prophet (peace be upon him) said: “The prayer of those who are repentant is observed when your weaned camels feel the heat of the sun." 

Why it is recommended to pray Duha? 

Duha Prayer has many virtues and rewards among them are the follwoing:

1- It fulfills charity on every joint in your body.

The Prophet (peace be upon him) said: "In the morning, every single joint of yours must pay a sadaqah (charity). Every SubhanAllah is a sadaqah, every Alhamdulillāh is a sadaqah, every La Ilaha Illa Allah is a sadaqah, every Allahu Akbar is a sadaqah, every commanding good is a sadaqah, and every forbidding evil is a sadaqah, and all this is accomplished through two rakʿahs one can pray in Duha [prayer]." (Muslim) 

2- It was an advice from the Messenger himself.

Abu Hurayrah reported: My beloved (the Prophet) advised me to do three things, which I will never abandon so long as I live: to fast three days of each month, to pray two rak`ahs of Duha prayer, and not to sleep until I pray Witr." (Al-Bukhari) 

And Allah Knows best.